This invention relates to the melting of materials. More specifically, the invention relates to the melting of glassy materials with oxy-fuel burners.
The glass industry has utilized air-fuel burners to melt glass and glassy like materials over the years. The developed processes included the use of submerged air-fuel combustion burners. These burners were located in the bottom or side wall of the furnace below the melt line. The advantages looked for in submerged combustion were increased heat transfer from the flame and the avoidance of high flame temperatures on the crown of the furnace.
In operation, the high volumes of air-gas resulted in open tunnels or chimneys up through the glass. The unstable nature of these xe2x80x9cchimneysxe2x80x9d resulted in their partial collapse or blockage with molten glass. The high volume of combustion gases from the vertical bottom entering burners and the parallel side entering burners result in rapid expulsion of gobs of glass in all directions. Some additional disadvantages observed included difficult maintenance of the burners, splashing of the glass over the crown with subsequent attack, a dirty off gas stream, difficult recuperation, and a very noisy operation.
While these early attempts focused on the flame temperature-heat transfer opportunity, they apparently failed to take into account the local effects of the heat transfer and the rather high kinetic energy of the flame and its transfer to the glass on the refractory structure and the fluid flow pattern of the melt volume. These localized effects resulted in very hot refractories adjacent to the burners as well as significant xe2x80x9cwashing-outxe2x80x9d of the refractories due to the high velocity of the glass in this same area. Some of those disadvantages result from using stationary burners in the vertical position. In the bottom location, the high kinetic energy of the combustion stream results in ejection of glass at high velocity all over the furnace crown.
In the prior art process, all of the required melting heat was supplied through the submerged burners.
This invention employs assemblies which include burners that use oxygen-fuel (oxy-fuel). The burners are water cooled top down units with burner nozzles being positioned in such away so as to maximize transfer of heat and kinetic energy from the combustion stream to the glass and utilizing this transferred kinetic energy, without the deleterious effects of the earlier efforts. Preferably, I submerge the burners in the molten material. However, in one embodiment, the burners are slightly above the molten material. The apparatus of this invention utilizes one or more burners for each top-down supply column. The supply column and attached burners can be rotated or moved in a manner to avoid the open chimney effect seen with stationary air-fuel burners of the prior art.
The mass flow rate to be used in these burners has, as a minimum, that required to stir the glass effectively. When it is desirable to minimize glass explusion, the maximum desirable flow rate is just below that which creates open tunnels or chimneys in the molten glass. This maximum flow rate can be greatly increased by the mechanical motion of the nozzle. Further, the mechanical movement of the burner nozzle extends and attenuates the hot gas path in the melt. This increases contact time and surface area for improved heat transfer. The movement also allows the glass to absorb more of the kinetic energy. All additional heat is made up from top fired burners.
These assemblies with an off-set nozzle like the letter L can be rotated at high speed to distribute the combustion in the form of gas bubbles or a gas curtain. In all applications, the high kinetic energy of the combustion stream coupled with the angle of the supply arm and the offset angle of the nozzle is utilized to induce favorable rapid flow of the melted glass. The combustion and subsequent glass flow are directed to avoid immediate impingement on the refractory structure of the furnace. The top down burners can be easily adjusted in depth for maximum effect, removed for repair, and started easily by firing above the batch until it melts and then lowering them down.